Permanent-magnet synchronous motors of this type are used for example in drive means of motor vehicles, in particular in power-assisted steering systems and the like.
FIG. 1a-c show generally known power-assisted steering systems by way of example. FIG. 1a shows a power-assisted steering system of a motor vehicle having wheels 106 which are steerably connected via a track rod 107. The track rod 107 cooperates with a steering gear 101, which in this case comprises a toothed rod (merely indicated symbolically by a double-headed arrow) which is connected to a pinion 105. The pinion 105 is rotatably coupled to a steering wheel via a steering shaft 102. A steering drive 103 in the configuration of an electric three-phase motor having a control unit 104 is attached to the steering gear 101, and assists in steering processes by cooperating with the toothed rod. FIG. 1b shows a power-assisted steering system similar to FIG. 1a, in which the steering drive 103 cooperates assistively with the steering shaft 102. The steering drive 103 may be attached to a steering column for this purpose. FIG. 1c likewise shows a power-assisted steering system similar to FIGS. 1a and 1b. In this configuration, the steering drive 103 is shown in cooperation with the pinion 105, and can also be arranged on the steering gear 101.
FIG. 2 is a schematic plan view of a permanent-magnet synchronous motor which is currently used as a steering drive 103 and which comprises: a stator 201 having grooves 202 in which windings (not shown) are arranged; and a rotor 204 having permanent magnets 203 which in the present case are arranged inside the rotor 204 on the circumference thereof in the axial direction of the motor. The rotor 204 is located inside the stator 201.
A motor of this type has to meet two main criteria, namely efficiency and safety. Parameters such as power intensity, maximum output torque, torque fluctuation or undulation, and detent torque or intermittent torque are of significance for the efficiency. The following parameters are of great importance for safety: maximum braking torque, short-circuit capacity, fault tolerance and simplicity.
The increased requirements on the conditions of use in a motor vehicle, in particular as regards a minimal constructional volume, weight, and number of individual parts used and a simultaneous high efficiency, and the above-mentioned parameters result in a constant requirement to provide a correspondingly improved permanent-magnet synchronous motor.